Litz wire for high-frequency coils wound with water-repellent textile fibres

ABSTRACT

In high-frequency coils wound from litz wires which each comprise a plurality of strands which each have a diameter of less than 50 Mu m, the strands being insulated from one another (enameled) and being wound round with threads consisting of textile fibres, corrosion damage due to defect in the enamel coating are prevented by impregnating the threads with a wetting water-repellent agent which is a thin liquid at room temperature, for example undiluted chemically pure paraffin oil or a mixture of methacrylate, dimerised rosin, Japan wax and enamel petrol, the spaces between the thread layers not being filled with the agent.

United States Patent 91 Ferber et al.

[ Jan. 1, 1974 (73] Assignee: U.S. Philips Corporation, New

York, NY.

22 Filed: Aug. 18, 1972 211 Appl. No.: 281,72l

[30] Foreign Application Priority Data Sept. 25, 1971 Germany P 21 48 057.9

{52] US. Cl. 174/121 A, 174/112, 174/114 R, 336/207 [5]] Int. Cl. H0lb 7/28 [58] Field of Search l74/l 14 R, 114 S,

174/12] R, 121 A, 121 SR, 112; 336/207- [56] References Cited UNITED STATES PATENTS 1,996,186 4/1935 Affler 174/114 R 2,479,186 8/1949 FlooX 174/114 S Primary Examiner-15. A. Goldberg Att0rneyFrank R. Trifari [57] ABSTRACT In high-frequency coils wound from litz wires which each comprise a plurality of strands which each have a diameter of less than 50 ,um, the strands being insulated from one another (enameled) and being wound round with threads consisting of textile fibres, corrosion damage due to defect in the enamel coating are prevented by impregnating the threads with a wetting water-repellent agent which is a thin liquid at room temperature, for example undiluted chemically pure paraffin oil or a mixture of methacrylate, dimerised rosin, Japan wax and enamel petrol, the spaces between the thread layers not being filled with the agent.

4 Claims, 3 Drawing Figures 1 urz WIRE FOR HlGH-FREQUENCYCOILS wouun WITH WATER-REPELLENT TEXTILE r BREs The invention relates to a litz wire for high-frequency coils which comprises a plurality of strands which each have a diameter of less than 50 um, are insulated from one another and together are wound round with at least one thread made of textile fibres.

Such litz wires are used to wind high-frequency coils of high electric quality. The textile covering ensures the mechanical bond of the litz wire and hence the exact structure of the coils wound from it and on the other hand increases the turns spacing. These two factors determine the electric properties, for example quality and self-capacitance.

Examples of textile fibres used are silk, artificial silk and cotton. A litz wire wound around with a textile material has the disadvantage that the electrical properties of a coil wound from the litz wire, which in themselve are good, are appreciably impaired by the fact that the textile fibres absorb moisture from the air. This process, which in itself is reversible, has the troublesome side effect that especially in industrial regions, in coastal areas and at sea corrosive constituents, such as sulphur compounds and halogen compounds, are absorbed from the air together with the moisture. Litz wires the individual strands of which have diameters of less than 50 um and are protected by a correspondingly thin by no means perfect layer of enamel, are heavily damaged by the contaminations in course of time, whilst litz wires the individual strands of which have diameters of at least 50 urn may be coated with correspondingly thicker layers of enamel, with a consequent reduction in the number of defects. Thus the advantage of the use of thin strands is offset by the disadvantage of its increased likelihood of faults.

If, in addition, in the circuit arrangement used an electric potential different is produced between separate windings of the coil or between the coiland its surroundings, the contamination which together with the moisture absorbed forms an electrolyte solution may cause complete failure of the coil and hence of the aaparatus within a short time/This is the case, for example, when owing to transistorisation and miniaturisation partial windings of a coil having different directvoltage potentials are superimposed on one another in a winding space.

it is common use for electrical components, including coils, to be shielded from the ambient atmosphere either by being arranged in an airtight metal housing or by being embedded in a synthetic resin, wax or the like which encloses all the parts of the coils except the terminals. Such methods are either too expensive for mass-produced articles, such as coils for radio receivers, or cannot be used for other reasons, for example because the coils after being mounted in the apparatus are to be trimmed and hence must be accessible even through a metal screening can. Experience has shown that partial enclosure, i.e. enclosure of the winding proper only, does not produce a seal but only delays the penetration of moisture and contamination, which it then will hold the longer.

It is also known to impregnate a fibre-covered wire for electric conductors to render the covering impermeable to moisture. For this purpose a molten wax-like or pitch-like material may be used. The impregnating agent may also consist of a mixture of rosin, paraffin, beeswax and resinous oil. Petrol may be used as a solvent (German Patent Specification No. 473,603). Furthermore, weather-proof insulations for electric conductors are known which consist of textile materials rendered weatherproof by impregnation with dried vegetable oils, bitumen and the like (German Patent Specification No. 946,357). It is also known to use methacrylate dispersions as impregnating agents for electrically insulating textile fabrics (Canadian Patent Specification No. 762,540).

In the three aforementioned patent specifications the insulating problem as such or the problem of the resistance of the insulating layer against external influences is discussed. The high-frequency litz wires of the type mentioned at the beginning of this specification are made up of strands provided with previously applied insulating layers. Hence the invention does not relate to a method of improving and sealing the insulating layers, for the winding of threads round the litz wire braided from insulated strands does not serve as an additional insulation. For this purpose this covering would have to be as dense as possible, but this would be at variance with the requirements of winding technology. By way of contrast the covering which generally is referred to as open and consists of a single textile thread wound with a pitch such that the litz wires are covered partly only has proved highly satisfactory. A covering of this type provides optimum results in that it hardly impairs the flexibility of the litz wire. The bunch of strands is held together and there is a suffi cient number of spaces in the coil which are filled with air, i.e. with the best dielectric possible. This optimum result obtainable as such is greatly impaired by the hydroscopic properties of the textile fibres, in particular the natural-silk fibres.

In the textile industry methods are known of eliminating or at least reducing the water-absorbing power of fibres by impregnating them. This may be effected in two manners. Fabrics may be charged or coated with linseed oil, synthetic rubber or plastics so intensively that the pores are closed and the fabrics become water-proof in the true sense of the word. On the other hand there are means and methods by the use of which the textile materials remain permeable to air but only their water-absorbing power is eliminated. This is referred to as a water-repellent covering or when highly wash-fast effects are obtained as hydrophobation. V

The water-repellent finishing is obtainable by applying hydrocarbons for example paraffin or waxes, either as such or in the form of solutions or emulsions, or by impregnating with metallic soaps or with paraffin or Wait emulsions containing metallic salts. Hydrophobation is obtained by chemical conversion with the fibre or by the application of synthetic resin derivatives, silicones or fluorine compounds (Ullmann Enzyklopaedie der technischen Chemie, 3rd Edition, Volume 17 (1966) pages 203-207). Water-repellent finishing by means of polyacryl synthetic resins also is known (L.Diserens, Neue Verfahren in der Technik der chemischen Veredelung der Textilfasern", Volume 3, Birkhauser Verlag, Basie/Stuttgart (1957), pages 692-695).

Thus in the textile industry the water-absorptivity of fibres is eliminated or reduced in two manners. In the the said properties being lost.

Finally a method of insulating thin wires for radio coils by means of thin layers of separate threads of artificial silk is known in which the individual threads before being wound around 'the strands are coated with hydrocarbons, for example paraffin oil (German Patent Specification No. 679,980). Thus a completely covered bare copper wire is manufactured the covering of which forms the insulation. The hydrocarbons are provided to prevent the production of electric charges which may cause the individual artificial-silk filaments to break during the process of covering. That the said specification does not refer to water-repellent effects will be clear from the sole fact that according to this Specification it is immaterial whether the hydrocarbons remain in the covering or are removed therefrom.

It is an object of the present invention to provide a high-frequency covered litz wire which ensures that the optimum electric properties are maintained but on the other hand prevents the occurrence of corrosion phenomena.

According to the invention this is achieved in that the thread made of textile fibres which is used for the covering is impregnated with a, wetting water-repellent agent which is liquid at room temperature, whilst the spaces between the threads are not filled with the agent.

A suitable water-repellent agent is an undiluted chemically pure paraffin oil of the type commercially available for spectroscopic purposes, for example liquid paraffin oil Uvasol, article No. 71 16 of the firm of E. Merck, Darmstadt.

For litz wires composed of solderable copper enameled threads the water-repellent agent in another embodiment of the invention has the following composi tion:

from 25 to 80 percent by weight of a 10 percent by weight methacrylate solution in enamel petrol (boiling range from 140C to 200C),

from 10 to 40 percent by weight of a l percent by weight solution of dimerised rosin in enamel petrol,

from to 35 percent by weight of Japan wax (melting point between 45C and 53C).

This mixture also improves solderability. It is used at a temperature between 28C and 34C.

For special purposes the water-repellent agent may be mixed with an identification dye. Suitable dyes are, for example, Ceres dyes and Sudan dyes, such as Ceres Blau GN (Farbenfabriken Bayer), and fat dyes, such as Fettrot G (Farbwerke Hochst).

The textile thread or threads may be impregnated either before they are wound around the copper conductors or on completion of the litz wire on the covering machine, but if required it may be effected as a separate step before the operation on the winding machine.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 is an elevation of an open covered litz wire comprising six strands;

FIG. 2 is a cross-sectional view of the litz wire of FIG. 1, the strands being designated by l and the covering threads by 2;

FIG. 3 shows a high-frequency coil made from the litz wire according to the invention. A coil former is designated by 3, a main winding by 4 and a coupling winding wound directly on the main winding by 5. The aforementioned potential difference may be produced between the main winding and the coupling winding.

The invention provides the following advantages.

1. The flexibility of the litz wire is increased, enabling windings to be obtained the uniformity of which is greater than has been possible hitherto. The resulting coils have considerably smaller spreads of the electric values. Hence final testing may be restricted to sampling.

2. The agent according to the invention enclosed the individual fibres of the textile thread without causing them to stick together and does not fill the spaces between the turns of the coil, because it is a thin liquid having good wetting properties.

3. It is true that the penetration of moisture in coils made by means of the litz wires according to the invention is not prevented, however, the moisture may read? ily escape, even at a rate higher than if the fibres were not impregnated, because their surfaces are waterrepellent.

4. Any corrosive impurities already present on the textile fibre are encapulated by the impregnating film, and penetrating impurities cannot become active because of the absence of solvents.

5. The solderability of the litz wires which are covered with natural silk and are composed of stands insulated by means of polyurethane enamels is not affected by the impregnation with the liquid paraffin oil. Hence in most cases it is not necessary to use as a waterrepellent a solution of resin which, although it improves the solderability, has a slightly weaker protective effect against corrosive attack.

What is claimed is:

l. Litz wire for high-frequency coils which comprises a plurality of strands which each have a diameter of less than 50 um, are insulated from one another and together are wound around with at least one thread made of textile fibres, characterized in that the textile thread is impregnated with a wetting water-repellent agent which is a thin liquid at room temperature, the spaces between the thread layers not being filled by the agent.

2. Litz wire as claimed in claim 1, characterized in that the thread is impregnated with undiluted chemically pure paraffin oil of the type commercially available for spectroscopic purposes.

3. Litz wire as claimed in claim 1, characterized in that the thread is impregnated with a mixture of from 25 to percent by weight of a 10 percent methacrylate solution in enamel petrol with a boiling range from C to 200C, from 10 to 40 percent by weight of a 10 percent by weight solution of dimerised rosin in enamel petrol, and from 10 to 35 percent by weight of Japan wax with a melting point between 45C and 53C.

4. Litz wire as claimed in claim 1, characterized in that the water-repellent agent contains a dye.

2 3 33 w UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 783,17? Dated January 1, 1974 Inventor(s) FERBER, JOHANNES KAI-INT and GUN'IER JOST It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

r-f- W In the Abstract, line 2, "which each have" should be --each having-- line 5, corro" should be Corro- 7 line 6, "defect" should be -defects-- line 11, the" should be The-- line 12, after "layers" insert '-are-- Column 1, line 7, delete "which" (second occurrence) line 8, "have" should be having and "are" should be -andline 31, after "thin" and "perfect" insert line 40, "different" should be -difference-- line 57, after "example," insert Column 4, line 30, "encapulated" shouldbe. --encapsulated Page -2- Po-ww I v UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 78 3, 179 Dated January l 1974 Inventofls) WILHELM FERBER and JOHANNES KAI-INT and GUNTER JOST It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

a Claims 1-4 should read as follows: .1

--l. Litz wire for high-frequency coils comprising a plurality of strands each having a diameter of less than 50 um, said strands being insulated from one another and together beingwound around with at least one' thread made of textile fibres, said textile thread being impregnated with a wetting water-repellent agent which is a thin liquidat room temperature, the spaces between the thread layers not being filled by the agent.

2. I Litz wire as claimed in Claim 1 wherein said thread is impregnated with undiluted chemically pure paraffinoil of the type commercially available for spectroscopic purposes.

3. 1 Litz wire as claimed in Claim 1, wherein said thread is impregnated with a mixture of from 25% to 80% by weight of a 10% methacrylate, solution in enamel petrol with alboiling range from 140C to 200C, from 10% to 40% by weight of a 10% by weight solutionv of dimerised rosin in enamel petrol, and from 10% to 35% by weight of Japan wax with a melting point between 45C and 53C.

4. "Litz wire as claimed in Claim '1, wherein said water-repellent agent contains a dye.--

v "Signed and sealedthis 9th day of July 1974.

' (SEAL) Attest:

I McCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents 

2. Litz wire as claimed in claim 1 wherein said thread is impregnated with undiluted chemically pure paraffin oil of the type commercially available for spectroscopic purposes.
 3. Litz wire as claimed in claim 1, wherein said thread is impregnated with a mixture of from 25 to 80 percent by weight of a 10 percent methacrylate solution in enamel petrol with a boiling range from 140*C to 200*C, from 10 to 40 percent by weight of a 10 percent by weight solution of dimerised rosin in enamel petrol, and from 10 to 35 percent by weight of Japan wax with a melting point between 45*C and 53*C.
 4. Lintz wire as claimed in claim 1, wherein said water-repellent agent contains a dye. 